I have a server with arch linux running bind (named). My ISP imposed a gateway on me which is a combination modem/router. When I connect my server to the gateway and forward traffic, port 53 is closed to the outside world (I use the Shields up site). An nmap scan using another computer behind the gateway shows port 53 open. Furthermore, I have two routers and I can connect the server to a router and the router to the gateway and this works (port is open to world) so long as I am using dd-wrt firmware. I can't get the stock firmware to work. I would appreciate any help getting the server to work while connected directly to the gateway. Any tips or suggestions or ideas on how to trace or isolate the problem would be a big help. Thanks in advance

You can go to portforward.com, find your router model, and learn how to forward ports from it to your nameserver system.

Thank you for the response, Z038. Unfortunately my gateway is a generic model provided by my ISP. It is called Comcast business class business IP gateway. It is not on the portforward.com list. Anyways, the interface is simple and I think I am configuring the settings correctly. I have no problems with ports 25, 80, and 143. I have forwarded ports on a number of different routers and the process is pretty similar and straightforward. My suspicion is that the gateway is forwarding requests to my server but is blocking responses from the server. Since port 53 uses the udp protocol it seems that this would just show up on a scan as port closed. When I do an nmap scan on the gatway from behind it shows 53 as open which makes sense because it is acting as a dns server for its clients, a feature I don't think I can disable. My theory is that my nameserver responses are being confused with such client requests and that dd-wrt is using some system which solves the problem. I am hoping I can mimick the dd-wrt system somehow on my Linux server. Anyways, thanks again